Magnetostratigraphy

Magnetostratigraphy is a special way scientists use to figure out how old different layers of rock and soil are. It works by looking at the direction of Earth's magnetic field when these layers were formed long ago. Scientists take samples from these layers and study how the tiny bits inside have kept a memory of Earth's magnetic field direction.

This method is very helpful because some layers of rock don’t have fossils or other clear signs that help tell their age. By studying these magnetic directions, scientists can match up layers from different places and understand how they line up over time.

Magnetostratigraphy helped prove an important idea called the Vine–Matthews–Morley hypothesis, which is part of the bigger theory of plate tectonics. This theory explains how the big pieces of Earth's outer shell — called tectonic plates — move around and change over millions of years.

Technique

When the magnetic properties of rocks change in layers, they can help us learn about Earth’s magnetic field. Scientists study these changes to sort rock layers into groups. They look at whether the magnetic field was normal (pointing north like today) or reversed (pointing south). This helps them figure out the age of the rocks and understand old environments.

A polarity chron is a time period when Earth’s magnetic field stayed in one position, either normal or reversed. These chrons are labeled with numbers and letters. By taking samples from rocks and studying their magnetic directions, scientists can match layers from different places and estimate when events happened. This method also helps learn about how fast sediments settled, which can give clues about past climates and Earth’s movements.

Main article: reversals in the polarity of the Earth's magnetic field